What is the use of declaring variable inside constructor

Question

I was studying class based structure in Javascript

To say the least, I created a simple class

class something { 
  constructor() {
  var name = "somexyz"
  this.age = 13 
  } 

  somefunc () {
    console.log(this.name)//Undefined
    console.log(name) //blank space
    console.log(this.age) //13
  }
}

And then call it using

let foo = new something()
foo.somefunc()

Which consoles.log (mentioned in comments of above code) 1. undefined 2. empty space 3. 13

or take a constructor function

function something () {
  this.age =  11
  let age = 13 
  this.getAge = function () {
   return this.age
  }
}

Here,

let somethingNew = new something() 

Will return age as 11

Now, my question is what exactly is the purpose of having variable in constructors then?

Answer 1

The emphasis should be on "simple class" - the notion of a local variable seems pointless but it's actually very useful.

Simple example - when you reuse a variable repeatedly

class transport
{
    constructor ()
    {
      const someString = "IUseThisAgainAndAgain";
      this.type = 'someType';
      this.name = 'someName';
      this.serial = someString + "SOMETHING";
      this.model = someString + "something thing";
      this.example = someString + "another string concat";
    }
}

As you can see we use someString alot. And you will see constructor method that are huge and having a variable for a repeated instance will allow better readability of code and allow you to easily modify the instance in one place.